A gravitational bending of light by structures in the Universe that distorts the
images of distant galaxies. The distortion allows the distribution of
→ dark matter and its evolution with time to be measured,
thereby probing the influence of → dark energy
on the growth of structures. Weak gravitational lensing is
generally difficult to identify in individual images, in contrast to
→ strong gravitational lensing
(see, e.g., Bartelmann & Peter Schneider, 2001, Phys. Rept. 340, 291).